Bone marrow adipose tissue composition following high-caloric feeding and fasting

Background: Bone marrow adipose tissue (BMAT) plays a role in systemic energy metabolism and responds to nutritional changes. Chronic starvation as well as visceral adiposity are associated with BMAT accumulation. Two types of BMAT have been described which differ in anatomic location (proximal-regulated-rBMAT vs distalconstitutive-cBMAT) and composition (higher unsaturated lipids of cBMAT compared to rBMAT). Objective: To determine the response of BMAT composition to short-term high-caloric feeding and fasting. We hypothesized that high-feeding and caloric restriction would be associated with differences in BMAT composition according to the skeletal site. Materials and methods: We examined 23 healthy subjects (13 m, 10 f, mean age 33 +/- 7 years, BMI 26 +/- 1.5 kg/m2) who were admitted for a 10-day high-caloric stay (caloric intake with goal to achieve 7% weight gain) followed by discharge home for 13-18 days to resume normal diet (stabilization period), followed by a 10-day fasting stay (no caloric intake). Subjects underwent single voxel proton MR spectroscopy (1H-MRS) at 3T of the lumbar spine (L4) (rBMAT), the femoral diaphysis and distal tibial metaphysis (cBMAT) to determine BMAT composition (unsaturation index, UI and saturation index, SI). Within group comparisons were performed by the Wilcoxon signed rank test. Results: After the high-calorie visit, SI of L4 increased compared to baseline (0.62 +/- 0.27 to 0.70 +/- 0.28, p = 0.02), and there was a trend of an increase in femoral SI and UI (p > 0.07), while there was no significant change in tibial BMAT (p > 0.13). During the stabilization period, SI of L4 decreased (0.70 +/- 0.28 to 0.57 +/- 0.21, p < 0.0001) and SI of the femoral diaphysis decreased (5.37 +/- 2.27 to 5.09 +/- 2.43, p = 0.03), while there was no significant change in UI or tibial BMAT (p > 0.14). During the fasting period, SI of L4 increased (0.57 +/- 0.21 to 0.63 +/- 0.30, p = 0.03), while there was no change in UI (p = 0.7). SI and UI of femoral diaphysis decreased (5.09 +/- 2.43 to 4.68 +/- 2.15, p = 0.03, and 0.62 +/- 0.42 to 0.47 +/- 0.37, p = 0.02, respectively) and UI of the tibial metaphysis decreased (1.48 +/- 0.49 to 1.24 +/- 0.57, p = 0.04). Conclusion: 1H-MRS is able to quantify BMAT composition during short-term nutritional challenges, showing a significant increase in SI of rBMAT during high caloric feeding and a differential response to fasting with an increase in SI of rBMAT and a decrease in SI and UI of femoral cBMAT and decrease in UI of tibial cBMAT.